For the accommodation of freight on freight carrying aircraft, a lower deck and sometimes also an upper deck are fitted with a power driven conveyor system for loading freight supported on pallets into and out of the cargo areas. Typically, the conveyor systems include a plurality of longitudinally extending roller trays rotatably supporting free roller conveyor wheels therein. At spaced intervals, power driven rollers are provided for engaging the lower surface of the pallet to move the pallet along the roller trays. These power driven rollers usually allow the roller to be raised and lowered relative to the lower surface of the pallet so that in the event of a power failure, the power driven roller can be recessed to a retracted position and the freight moved manually along the roller trays.
Many such power driven roller assemblies are supported in a canister type housing and are mounted so that the roller is partially submerged below the surface of the floor. This is done so that the roller may be constructed of a sufficiently large diameter while not extending above the typically lower profile roller trays. In order to maintain a sufficient frictional contact with the lower surface of the pallet, the rollers are frequently pneumatic so that the resilient roller wheel itself will deflect upon encountering irregularities in the lower surface of the pallet, while continuing to maintain a sufficient frictional engagement with the lower surface of the pallet to drive the pallet along the roller trays. Examples of prior art devices constructed in this manner include the U.S. Pat. No. 3,899,070 to Lang, issued Aug. 12, 1975, U.S. Pat. No. 3,565,233 to Hinman, issued Feb. 23, 1971, U.S. Pat. No. 3,978,975 to Herbes et al, issued Sep. 7, 1976 and U.S. Pat. No. 4,589,542 to Steadman, issued May 20, 1986.
The prior art pneumatic roller which flexes with the regularities in the lower surface of the pallet are deficient in that severe irregularities may either over burden the roller and cause a rupture or may diminish frictional contact to a point where slippage occurs between the roller and the lower surface of the pallet. Also, as the roller flexes with the irregularities in the lower surface of the pallet, the distance between the rolling axis of the roller and the point of engagement of the lower surface of the pallet varies such that the linear velocity imparted to the pallet varies. As a result, the pallet is not smoothly conveyed over the roller trays.